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Raised Bed Soil Guide

by Molly Carney December 17, 2020 4 min read

Raised Bed Soil Guide

Did you know soil is extremely complex? It’s not just a filler for your garden bed that holds your plants upright. Soil is full of living organisms, and it’s where your plants get their nutrients. Your soil performs many jobs – it’s where your plants find stored water when you forget about them, and it also helps excess water to drain. It’s packed full of bacteria, good and bad. The soil you use to grow your vegetables will determine if you have a bountiful crop or a struggling crop. Let’s look at some ways to get your soil packed full of nutrients, minerals, and all the components needed for your garden to thrive.

The bulk of your soil should be topsoil, making up 50-60% of your garden bed. Topsoil can be purchased in bags in a garden center or in bulk from a local topsoil supplier. Look for organic topsoil that is dark in color and soft to the touch. Some brands will add in wood chips or the soil will be too clumpy.

Compost should make up around 30% of your garden bed soil. Compost is packed full of good bacteria and nutrients that will provide your plants with the food they need to grow and thrive. Every compost is different, so adding several different kinds of compost will give your garden a diversity of minerals and nutrients. Compost can be bought in bags at a garden center or big box store, but buying in bags will most likely be the most expensive option. Some local garden centers might have compost to purchase in bulk. You can also purchase compost from a local topsoil/mulch supplier.

The last 10% of your garden bed soil should be made up of equal parts of a drainage substance and water retention substance. The most common substance that promotes drainage is perlite and vermiculite. If you’ve ever bought potting soil from a bag and noticed small white Styrofoam-looking pieces, that’s perlite. Perlite is made from Volcanic glass that is heated up until it explodes into little white pieces. Perlite helps make the soil lighter and allows air to get to the roots of your plant. It’s best to add to plants that do not need a lot of water. Another substance that promotes drainage is Vermiculite. Vermiculite helps both with water retention and drainage. It mimics a sponge by soaking up water, then allows drainage when it is saturated with water. Vermiculite also helps with nutrient retention. Along with a substance to promote drainage, a substance to promote water retention is equally as important to the soil. A product that you can add to your soil to help with water retention is peat moss. Peat moss holds water, then releases it slowly to the roots as they need it. Peat moss also holds onto nutrients in the soil so they aren’t washed away when you water your plants. Coconut coir can also be added to help retain water, reduce compaction, and help with drainage.

While the base of your soil should be topsoil, compost, drainage, and water retention, there are more things you can add to your soil, such as rock dust. Rock dust is full of trace minerals. Another way to boost your soil is by adding worm castings. Worm castings can add five times the nitrogen to your soil, ten times the potassium, and seven times the phosphorus. Worm castings can also help give plants immunity against diseases. In addition to adding nutrients to your soil and helping your plants to grow, they also help to retain water. A third great addition to your soil is biochar. Biochar puts nutrients back into the soil and creates a good environment for the good bacteria and fungi to grow. Just as our bodies flourish with many different vegetables and fruits to give us a wide range of nutrients and minerals, your garden will also flourish when grown in diverse soil.

The finished cost of your soil can vary quite a bit. If you are looking for the most convenient and easy way to add great soil to your garden, you will be spending a little more. Buying in bulk is always cheaper than by the bag. If you are willing to shop prices in your area and learn how to make your own compost, you’ll save money. Homemade compost will require some research and time to develop, but it’s great for garden beds!

The most convenient way to get great soil is to buy it already pre-mixed. There’s a great mix called “Mel’s Mix”. It is compost, drainage product, and water retention product already mixed together. Mel’s Mix is 40-50% compost, vermiculite, peat moss, coir, with additions of worm castings, bloodmeal, bone meal, and kelp meal. You can buy Mel’s Mix in two cubic feet bags. You can also buy all the ingredients separate at a garden center and mix them together yourself. If you are solely looking for convenience, you can order most of these products on amazon.

Soil is the environment where your plants find their food and oxygen. It’s where water is stored so that your plants can continually get replenished. Great soil will protect your plants from disease, and provide an environment of good bacteria. Whether you buy your ingredients and mix it yourself, or buy it premixed, make sure you follow the rough ratios of 50-60% topsoil, 30% compost, 10% drainage and water retention product, and any extras you choose (rock dust, biochar, worm castings). If your plants eat well and thrive, you will eat well and thrive!

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